Corner Reflectors
Corner reflectors are used for the geometric and radiometric calibration and verification of Synthetic Aperture Radar (SAR) sensors. Their expected position in a focused SAR image and their expected backscatter coefficient are unambiguously defined if the geodetic position of their phase centres (which coincide with the inner corner of the reflector) and the edge lengths are known.
Measuring the unprecedented, centimetre-level pixel localization accuracy of the German TerraSAR-X satellites TSX-1 and TDX-1 requires precise knowledge of a corner reflector’s ground position. In order to satisfy this requirement, a test site in the vicinity of an IGS reference station, as is the case at GARS O’Higgins, allows the position on the ground to be measured with high accuracy (< 5 mm) relative to the reference station’s coordinates obtained by terrestrial geodetic survey.
In March 2013, two trihedral 0.7 m corner reflectors were installed at GARS O’Higgins within the framework of the HGF Munich Aerospace “High Resolution Geodetic Earth Observation” project. These corner reflectors are part of a network of widely-distributed test sites – the others are in Wettzell, Germany and Metsähovi, Finland – whose purpose is to evaluate the localization accuracy of TerraSAR-X mission data and assure global comparability of measurements. The GARS O'Higgins site plays a key role in the project because its extreme southern position puts it at a beneficially large distance from the two Northern Hemisphere sites.